Project Summary Adverse drug reactions (ADRs) are a relatively common cause of morbidity and mortality with hypersensitivity reactions accounting for approximately 25% of these ADRs. Drugs are the most common cause of fatal anaphylaxis and cephalosporin antibiotics have been the most commonly identified culprit drugs in many studies in the U.S. A label of antibiotic allergy is common in the general population and a majority of hospitalized patients are treated with antibiotics. An inaccurate label of antibiotic allergy can adversely affect the quantity and quality of health care use. Penicillin skin testing has been utilized in the evaluation of patients with suspected IgE-mediated reactions to penicillin since the 1960's and the negative predictive value of penicillin skin testing has been shown to be 97-99% in large-scale studies. In addition, several studies have shown improved health outcomes after penicillin skin testing. Cephalosporins are widely used antibiotics that share a beta-lactam ring and sometimes side chains with penicillins. A reported allergy to penicillin and/or cephalosporin has been associated with a higher use of other broad-spectrum antibiotics. Cephalosporin skin testing unlike penicillin skin testing has not been validated as a method for evaluation of cephalosporin allergy. The mechanisms and specific antigens that drive both class and side-chain specific cephalosporin IgE mediated reactions have not been elucidated. We propose to perform a prospective multicenter U.S. study that will be the first adequately powered study of cephalosporin diagnostic tests. We will enroll subjects with histories of immediate reactions to cephalosporins grouped according to their side chain structure and powered on a primary outcome of negative predictive value of cephalosporin skin testing. In our study design, we include cephalosporin challenges in properly selected subjects as our ?reference standard?, so that our index test (skin testing) can be properly validated. In Aim 1 we will determine the optimal diagnostic approach to removing the label of cephalosporin allergy. Identifying which patients can be challenged without prior need for skin or in vitro tests and those who would benefit from skin or in vitro testing prior to challenge will be determined. Aim 2 will investigate if a novel nanoallergen platform will enhance detection and functionality of specific IgE in patients with confirmed cephalosporin allergy. The nanoallergen platform will also be utilized to gain insights into important cephalosporin epitopes. In Aim 3, we will investigate the genetic variation of immediate allergic reactions associated with cephalosporins. We will obtain DNA from cephalosporin allergic, skin test negative and tolerant subjects for high resolution HLA ABC DR DQ DP typing and genome wide association studies. A replication cohort will be enlisted to reproduce these findings. The goal of this proposal is to develop the complete research group, study protocols, study infrastructure and data capturing tools. In the last 6 months of this award, preparation of the U01 for this multi-center clinical trial will occur. !